1. Technical Field
This invention relates generally to the testing of electronic devices, including circuit boards, semiconductors, and hybrids, in addition to the batch processing of miniature electronic circuit components, including passive, two-terminal, ceramic capacitors, resistors, inductors, and the like. More particularly, it concerns a contactor assembly for electrically contacting a terminal on any device under test (DUT), including, circuit boards, hybrids, semiconductors, and passive components, as part of the batch processing for purposes of parametric testing.
2. Description of Related Art
Continuous miniaturization and the resulting shrinking geometries found within semiconductors, hybrids, and circuit boards, in addition to the tiny size of electronic circuit components of interest herein, complicates processing. Features within semiconductors, hybrids, and circuit boards can be only a few microns in size, and in some cases, even sub-micron. Passive components are typically fabricated in parallelepiped shapes having dimensions as small as 0.020″ by 0.010″ by 0.010,″ more or less, these difficult-to-handle components require appropriate equipment and precision handling techniques. What is sometimes referred to as a “carrier plate” holds many hundreds of the components upright in spaced-apart positions as the ends of each component are coated with a conductive material to produce electrical terminals. After adding terminals, a “test plate” holds the large batch of components for movement past a contactor assembly of a testing system for parametric testing purposes and eventual sorting. Thoughtful design of each of these components promotes efficient processing. Reference may be made to U.S. Pat. Nos. 6,204,464; 6,294,747; 6,194,679; 6,069,480; 4,395,184; and 4,669,416 for examples of some prior art component handling systems and testing techniques.
The contactor assembly is of particular interest. It is a device having an electrical contact that touches the DUT terminal as the test plate or other handling device moves the DUT past the contactor assembly. It does so to complete an electrical testing circuit. One problem is that touching the DUT terminal improperly can physically damage the terminal. It can also produce a poor electrical contact that degrades test results. U.S. patent application Ser. No. 10/097,464 addresses those concerns with a multi-contact contactor assembly that can be implemented with sliding contacts, rolling contacts, or pogo pin contacts.
As mentioned in the above-identified patent application, the electrical and mechanical functions of the contactors are conflicting and this holds true for pogo pin contactors (or probes). The electrical function is to deliver the test signal to the terminal of a DUT so that an accurate test can be performed. The mechanical function is to push a contact against the DUT terminal with enough force to break through any non-conductive surface layer on the DUT terminal so that a low resistance contact can be achieved, thus enabling an accurate test. Breaking through the non-conductive layer can leave a scratch, indentation, or other mark which may be considered a defect by the end user of the DUT. On the other hand, not breaking through the non-conductive layer may prevent a good contact (low serial resistance) and result in an inaccurate test result.
The electrical and mechanical functions in typical existing pogo probes are closely integrated and cannot be separated. There are several reasons for this. First, the pogo spring resides within the probe itself. This automatically limits the size, shape, and length of the spring that can be used and it usually means that the spring is very small and therefore rather fragile. In fact, one of the main failure modes for existing pogo probes is the spring breaking during use.
Second, the spring inside the pogo probe is a compression spring, that is, it is designed to be compressed in normal use. When one looks at a compression spring when it is in the relaxed (non-compressed) state, it looks very much like, and is, an air wound inductor. Having an inductor inside the probe can introduce uncontrolled stray impedances for which the user cannot compensate. Many elaborate designs have been introduced to reduce this undesired characteristic.
Third, most existing pogo probes do not allow for a Kelvin circuit within the contact. A common technique is to use two probes, one for drive and one for sense, thus doubling the number of probes to be used, maintained, cleaned, aligned, and so forth. Since these probes do not allow for Kelvin testing, the contact tips must break through any non-conductive layer to achieve a low resistance contact to the DUT terminal. Many existing probes have pointed or spear shaped tips for this purpose. Such tips can easily cause damage to the DUT terminal.
In addition, since typical existing pogo probe designs tightly integrate the mechanical and electrical functions, there is no way to quickly change the probe tip without changing the entire probe assembly. That fact introduces costs and inconvenience.
Furthermore, discreet devices, circuit boards, hybrid assemblies, semiconductors, and so forth are constantly evolving into more miniaturized configurations. As they become smaller, the geometry of the individual elements within the devices become smaller, resulting in a requirement to locate and place a test contact with more precision and repeatability. Careful design of the contactor assembly and the test plate help control positioning of the contactor assembly relative to the DUT terminal, but existing positioning techniques need improvement.